The present invention relates to a process for separation of metallurgical products, such as steel billets, blooms or small slabs, and more particularly to the cutting of these products into selected lengths, while reducing the adherence of slag on cut edges of the products.
In a continuous casting operation, a continuous cast strand is cut into lengths, such as steel billets, using an oxygen-fuel cutting torch system. Oxygen-fuel cutting torch systems are well known and are commonly used in the cutting and welding industry. A cutting torch is mounted to move with the cast steel strand and to make a lateral separating cut through the strand perpendicular to its longitudinal axis and its direction of movement.
Conventionally, the cutting torch is positioned above and moves longitudinally together with the steel strand while being driven in a straight path transverse to the steel strand. Thus, the cutting torch flame projects downwardly and is moved horizontally across the steel strand, thereby cutting the billet. During the cutting process, the cutting torch flame produces a kerf in the steel strand. Molten steel and iron oxide flow downwardly through the kerf and drop below the billet for collection and disposal. However, some of the molten steel and iron oxide adhere to the bottom edges of the kerf and form slag beads that accumulate along those edges. This slag must be removed; otherwise it adversely affects subsequent forming operations performed on the billets, which may cause defects in finished steel products made from the billets. For example, the slag beads may adhere to roller surfaces used for steel plate forming. Since the slag beads are much harder than the steel billet, the slag beads may form dimples in the rolled steel surface, or embed in the surface. However, removing the slag beads from the billet in a secondary operation, such as scarfing, is tedious, time consuming and costly. Therefore, efforts are generally made to immediately remove the slag accumulation during the cutting process.
In general, it has been discovered, and is well known that directing a fluid stream at the molten slag as it forms on the edges of the kerf tends to blow it away and thereby reduce its adherence. The fluid stream may comprise air, oxygen, water, mixtures thereof, or other gases or liquids. U.S. Pat. No. 4,336,078, entitled PROCESS AND APPARATUS FOR THE SEPARATION OF METALLURGICAL PRODUCTS, issued to Radtke on Jun. 22, 1982, for example, describes a process and apparatus for separating metallurgical products such as ingots, slabs or plate-shaped work pieces using a cutting torch deposed on one side of the product. The cutting torch follows a prescribed cutting line and forms a front cutting edge on the surface of the product facing the cutting torch, a rear cutting edge on the opposite side of the product, and a cutting joint therebetween. At least one gaseous jet is directed at the rear cutting edge of the product to blow away molten metal and liquid slag from the rear cutting edge during the cutting process, thereby preventing the formation of slag beads at the edges of the cutting joint.
As another example of the slag adherence reduction, U.S. Pat. No. 4,923,527, entitled APPARATUS AND METHOD FOR SLAG-FREE CUTTING OF BILLETS AND THE LIKE, issued to Ludwigson on May 8, 1990, describes a billet cutting apparatus of the type, which includes an oxy-fuel cutting torch. The apparatus includes a slag removal nozzle operative simultaneously with the cutting torch to direct a jet of oxygen along the lower edge of the billet to remove slag beads tending to form thereon. The oxygen nozzle has a unique opening configuration, which provides a thin, flat oxygen stream effective over a substantial distance, such that the nozzle can be mounted laterally of the billet and outside the hostile and potentially damaging environment created by the cutting torch and the hot billet. The oxygen nozzle may be conveniently mounted in a fixed position, and in an automated billet cutting apparatus, may be attached directly to one of the billet clamping arms.
Neither of these methods has achieved wide commercial success, however. Consequently, there is still a need for alternative technologies to minimize slag bead adherence during the cutting of steel billets, and the like.
It is therefore an object of the invention to provide a method and apparatus for cutting steel with a cutting torch, while reducing slag adherence to a cut edge of the steel.
It is another object of the invention to provide a method and apparatus for cutting steel, which minimizes slag formation by moving a cutting torch in an arcuate path to reduce the area where slag can accumulate on the cut edges.
In accordance with one aspect of the present invention, a method is provided for cutting steel with a cutting torch to reduce slag adherence to a cut edge of the steel. The method comprises steps of commencing a cut at a first side of the steel, and moving the cutting torch in a arcuate path shaped to continuously aim a cutting flame at a fixed point located at a bottom of a first side of the steel, and following the arcuate path to keep the cutting flame aimed at the fixed point until the steel is cut.
When the steel has a bottom surface and an angle of the bottom corner at the first side is not greater than 90xc2x0, it is preferable to move the cutting torch from the first side of the steel to a second side which is opposite the first side, while gradually rotating the cutting torch from a first orientation perpendicular to the bottom surface, and along the arcuate path to a second orientation parallel to the bottom surface of the steel, so that the cutting flame of the cutting torch is continuously aimed at the bottom corner of the first side of the steel. The cutting torch is preferably moved transversely relative to the steel, while being maintained stationary relative to a longitudinal axis of the steel. In particular, in continuous cast cutting operations, the cutting torch is moved synchronously with the steel in a direction parallel with the longitudinal axis of the steel. Thus, the molten metal and iron oxide, under the influence of the force of the cutting flame jet, flow toward the bottom corner at the first side of the steel as the cutting torch moves along the arcuate path and the cutting flame thereby pivots across the steel. Substantially all of the molten metal and iron oxide drop off below the steel, and only a very small amount of slag bead adheres to the bottom corner of the first side of the steel, which can generally be ignored in a subsequent forming process.
In accordance with another aspect of the invention, an apparatus is provided for cutting steel to reduce slag adherence to the steel. The apparatus comprises a cutting torch and means for moving the cutting torch in an arcuate path to ensure that a cutting flame of the cutting torch is always aimed at a bottom corner of the steel.
The means for moving the cutting torch preferably comprises a track forming the arcuate path for guiding the cutting torch movement, a drive mechanism operatively connected to the cutting torch to move the cutting torch along the track, and a frame to support the track and the drive mechanism. A linkage system is preferably included in the drive mechanism to convert a rotational movement of a rotating shaft into the movement of the cutting torch along the track.
In one embodiment of the present invention, a sleeve having internal threads is rotatably connected to the cutting torch about an axis perpendicular to both a plane determined by the track and a longitudinal axis of the sleeve. A drive shaft is provided which has a free end and an end connected by means of a universal joint, to the rotating shaft. The drive shaft has external threads that threadingly engage the sleeve. The drive shaft is pivotable about an axis perpendicular to the plane of the track and extends through the universal joint. Thus, when the rotating shaft rotates the drive shaft through the universal joint, the sleeve moves along the drive shaft and causes the cutting torch to move along the track. The drive shaft may be rotated by a motor mounted to the frame.
The frame may be movable along a path parallel to the longitudinal axis of the steel and include clamping means for releasably clamping the steel between the frames in a position in which a longitudinal axis of the steel is perpendicular to the plane determined by the track. Thus the cutting torch is moved together with the steel when, for example, the steel is a continuous cast strand exiting a caster.
In another embodiment of the invention, a rack and a pinion are provided to replace the motor for converting the movement of the frame into the rotational movement of the rotating shaft. The rotating shaft in turn rotates the drive shaft through the universal joint, thereby causing the cutting torch to move along the track. The rack is mounted to a stationary support, such as a track for supporting and guiding the movable frame. The pinion is affixed to the rotating shaft and is adapted to rotate together with the rotating shaft, which is rotatably mounted to the frame.
In accordance with a further embodiment of the invention, a double acting fluid cylinder and pivoting linkage system serve as the drive mechanism. The cylinder is pivotally mounted to the frame about an axis perpendicular to the plane of the track and is also pivotally connected to the cutting torch about an axis, which is also perpendicular to the plane of the track. Therefore, the cylinder pivots about its mounting axis and the cutting torch is urged along the track when the cylinder is operated in either direction.
The present invention advantageously provides an alternative technology for cutting steel with a cutting torch while reducing slag adherence to the cut edge without using a secondary nozzle to inject a fluid stream for slag bead removal.
Other advantages and features of the present invention will be better understood with reference to preferred embodiments of the present invention described hereinafter.